The present invention relates to a steering wheel cover having a multilayer structure adapted to be applied to a steering wheel of a motor vehicle. These steering wheel covers are used, by virtue of their construction, as part of an arrangement for detecting if a driver's hand is on the steering wheel by determining the impedance between an electrode within the steering wheel cover and the vehicle body by means of an evaluation unit.
Such a steering wheel cover has a multi-layered structure, which has in one plane a circumferential length and a cross-sectional (i.e., transverse) width. The circumferential length is associated with the outer circumference of a steering wheel rim to be covered with the steering wheel cover and the cross-sectional width is associated with the outer diameter, viewed in the cross-sectional direction of the steering wheel rim. The steering wheel cover has a multi-layered structure, wherein the layers cover each other, at least partially in projection.
The layer sequence comprises a lower, electrically conductive shielding layer pointing to the steering wheel core, followed, when viewed in the direction toward an upper cover layer associated with the outer steering wheel cover, by a shielding layer, an insulation layer and at least one electrically conductive sensor layer.
The shielding layer and/or the sensor layer have a conductor structure with conductors extending in the circumferential length and in the cross-sectional width; the shielding layer and the sensor layer are electrically connected to connecting conductors of a connecting cable.
DE 203 09 603 U1 describes a steering device, i.e., a steering wheel for a motor vehicle. The steering wheel has a sensor device, which is designed as a capacitive sensor element, which is located in the area of the steering wheel rim of the steering wheel. This sensor device serves the purpose of detecting the approach and/or contact of the steering wheel rim by a driver's hand by changing the capacitance of the sensor element in order to also determine if the hand of a vehicle occupant is completely or only partly on the steering wheel or is even only in the vicinity of the steering wheel and if the steering wheel is grasped by the complete hand or is only touched by individual fingers. The sensor device is covered by a steering wheel covering or a steering wheel casing made of a leather or plastic material and consists of a conductor arrangement, which may be designed as an electrically conductive wire wound around the steering wheel rim. This arrangement of conductors acts as a capacitive sensor device. The signals are captured by an electronic evaluation unit, which can be arranged in the central area of the steering wheel. The sensor device can also be constructed of a conductive network structure or flat ribbon conductors. In one embodiment, the steering wheel rim is divided into sections to enable a locally resolved detection. The conductor arrangement can also serve as a heating device.
DE 10 2009 058 138 A1 describes a method for producing a proximity sensor for a vehicle, which is intended for a steering wheel in a vehicle. This proximity sensor has an upper fabric layer with conductive warp threads incorporated therein, a lower fabric layer with conductive weft threads incorporated therein, and a central fabric layer of non-conductive threads, which isolates the upper from the lower fabric layer. The upper and the lower fabric layer are each connected to an evaluation unit via a connector. The total capacity of this arrangement is comprised of the capacity of the three fabric layers, as well as a capacity that varies with the distance of a finger or a hand from the arrangement.
DE 10 2011 084 903 A1 focuses on sensor systems for a motor vehicle that can also be installed in a steering wheel, which also includes a heating device, with a capacitive sensor element that is intended to avoid or minimize interference due to parasitic capacities. In the arrangement of this sensor element on the steering wheel rim of a steering wheel, which can also be heated, wherein the steering wheel rim is constructed from a metal skeleton surrounded by a dielectric material, a heating layer is positioned on the dielectric material, which is covered on the outer side by a shielding layer, followed by a sensor layer, which in turn is surrounded by a cover of the steering wheel. A heating conductor and/or a sensor conductor of the capacitive sensor element can be designed as sewing threads. A metal mesh that is formed by warp and weft wires can be used for the shielding layer.
Another sensor system for a steering wheel of a vehicle is described in US 2012/0326735 A1 and has a first sensor, which is arranged inside a left, front section of the steering wheel in order to detect a contact of the left front section of the steering wheel, and has a second sensor, which is arranged inside the right front section of the steering wheel in order to detect a contact of the right, front section of the steering wheel separated from the first section. Furthermore, a third sensor is provided that is associated with the back of the steering wheel to capture contact of the rear section of the steering wheel. Touching of the respective section associated with the three sensors by the hand of a driver can be detected, whereby a driver's touch that does not take place with the hand can also be distinguished. Complex impedance sensors can be used as the sensors.
DE 203 09 877 U1 is directed to a vehicle safety system in which at least one capacitive sensor, preferably a plurality of sensors, is/are integrated into the steering wheel rim of a steering wheel. A change in an electrical or electromagnetic field is detected via sensors. The sensors are located between the wrapping, for example, PUR foam around a steering wheel skeleton, and a wrapping closing the steering wheel to the outside in the form of a flexible layer of foam, or leather or wood wrapping. The sensors can also be formed by at least a section of a steering wheel heater. When several sensors are used, conclusions can be drawn about the position of the upper body or the head of a driver relative to the steering wheel's axis of rotation. The sensors can be built as a flexible mat with elongated electrical conductors integrated therein. Such a sensor can also contain a nonwoven mat.